The composition of exhaust produced by the combustion of hydrocarbon fuels includes a mixture of particulate matter (soot), oxide gases (such as, for example, NOX, SOX, etc.), and unburned hydrocarbons. To comply with emission standards, engine manufacturers have developed and implemented a variety of exhaust treatment devices to reduce pollutants in exhaust gas prior to the exhaust gas being released into the atmosphere. These exhaust treatment devices may include, for example, a diesel particulate filter (DPF), a selective catalytic reduction (SCR) device, a diesel oxidation catalyst (DOC), an NH3 oxidation (AMOX) device, and other similar components. These devices capture and/or convert undesirable constituents in exhaust gas into less harmful products as the exhaust gas flows through.
The long-term durability of the exhaust treatment devices is essential for efficient emission control. The durability of these devices can be affected by a variety of factors including engine lubricating oil consumption. For example, during normal engine operation, some of the lubricating oil may be combusted, and the deposition of combustion products from phosphorus-containing lubricant additives can adversely affect the durability of exhaust treatment devices in a process known as “phosphorus aging” or “phosphorus poisoning.” To minimize this adverse impact, engines are designed to reduce lubricant consumption, and lubricants are formulated with lower concentrations of phosphorus-containing compounds. However, phosphorus-containing lubricant additives (such as Zinc Dialkyl Dithiophosphate, or ZDDP) are necessary to protect the engine from excessive wear and assist in increasing engine durability. Historically, techniques such as oversizing an exhaust treatment device and regenerating an exhaust treatment device with the addition of scavenging additives have been used to combat phosphorus aging of exhaust treatments devices. However, these techniques typically increase the cost and/or complexity of the exhaust treatment system. While simply removing and replacing a phosphorous-laden catalyst is also an option, replacing the catalyst, which is composed of precious earth metals, can be an expensive operation.
Japanese Patent Application No. 60-26381 (the '381 Application) published on Feb. 1, 1994, discloses an engine control system that detects degradation of the catalyst due to phosphorus poisoning by measuring oil consumption, and adjusts the air-fuel ratio in order to curtail further degradation. While the method of the '381 Application may increase usable life of a catalyst, it has drawbacks. For instance, there may be delays associated with detection of catalyst deterioration and subsequent response. The delays would entail additional adjustments of air-fuel ratios in order to account for any additional deterioration that takes place during the delays. Additionally, the '381 Application does not provide options other than adjusting air-fuel ratio to address catalyst degradation. Furthermore, the '381 Application only measures an oil consumption to determine catalyst degradation without taking into account other relevant parameters such as engine pressure and temperature. This single-parameter approach may compromise the accuracy of the catalyst degradation measurements.
The disclosed exhaust treatment systems are directed at overcoming these and/or other shortcomings in existing technology.